Field of the Invention
The present invention relates to polypeptides having lysozyme activity, catalytic domains, and polynucleotides encoding the polypeptides and catalytic domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides and catalytic domains.
Description of the Related Art
Lysozyme is a O-glycosyl hydrolase produced as a defensive mechanism against bacteria by many organisms. The enzyme causes the hydrolysis of bacterial cell walls by cleaving the glycosidic bonds of peptidoglycan; an important structural molecule in bacteria. After having their cell walls weakened by lysozyme action, bacterial cells lyse resulting from osmotic pressure.
Lysozyme occurs in many organisms such as viruses, plants, insects, birds, reptiles and mammals. In mammals, Lysozyme has been isolated from nasal secretions, saliva, tears, intestines, urine and milk. The enzyme cleaves the glycosidic bond between carbon number 1 of N-acetylmuramic acid and carbon number 4 of N-acetyl-D-glucosamine. In vivo, these two carbohydrates are polymerized to form the cell wall polysaccharide.
There is an increasing interest in the potential of lysozyme enzymes as antimicrobial agents. For example, lysozyme activity has been shown against pathogens such as Streptococcus pneumoniae, Bacillus anthracis, Enterococcus faecium, Bacillus stearothermophilus, Clostridium botulinum, Clostridium butyricum, Clostridium perfringens, Clostridium sporogenes, Clostridium tyrobutyricum, and Listeria monocytogenes. 
Lysozyme has been classified into five different glycoside hydrolase (GH) families (CAZy, www.cazy.org): hen egg-white lysozyme (GH22), goose egg-white lysozyme (GH23), bacteriophage T4 lysozyme (GH24), Sphingomonas flagellar protein (GH73) and Chalaropsis lysozymes (GH25). Lysozymes from the families GH23 and GH24 are primarily known from bacteriophages and have not been identified in fungi. The lysozyme family GH25 has been found to be structurally unrelated to the other lysozyme families.
Use of lysozyme has been suggested in animal feed (see for example WO 00/21381 and WO 2004/026334), in cheese production (see for example WO 2005/080559), food preservation (Hughey and Johnson, 1987, Appl. Environ. Microbiol. 53:2165), detergents (see for example U.S. Pat. No. 5,041,236 and EP 0425016), in oral care (see for example U.S. Pat. No. 4,355,022, WO 2004/017988 and WO 2008/124764), cosmetology and dermatology, contraception, urology, and gynaecology (see for example WO 2008/124764).
A GH25 lysozyme has been reported from Chalaropsis (Felsch et al., 1975, “The N,O-Diacetylmuramidase of Chalaropsis species; V The complete amino acid sequence”, J. Biol. Chem. 250(10):3713-3720).
Hen egg white lysozyme which is the primary product available on the commercial market, does not cleave N,6-O-diacetylmuramidase in, e.g., Staphylococcus aureus cell walls and is thus unable to lyse this important human pathogen among others (Masschalck et al., 2002, “Lytic and nonlytic mechanism of inactivation of gram-positive bacteria by lysozyme under atmospheric and high hydrostatic pressure”, J. Food Prot. 65(12):1916-23).
It has been observed that different lysozymes have different specificities towards different microorganisms. It is therefore desirable to have several lysozymes available in order to be able to select suitable enzymes for each particular application. New polypeptides having lysozyme activity is therefore desired.